The present invention relates to an image forming apparatus of the type transferring a plurality of different kinds of data, e.g., a color digital copier or a color printer and, more particularly, to a data transfer device for such an image forming apparatus.
In a conventional data transfer device for. e.g., a bicolor digital copier, black data having tonality represented by eight bits (256 levels) are transferred from a black processing unit of a sending station to a black processing unit of a receiving station. Red data having tonality represented by one bit (two levels) is transferred from a red processing unit of the receiving sending station to a red processing unit of the station. Specifically, the black processing unit of the sending station separates 8-bit black data, i.e., "0" to "255" from RGB data representative of a document read. The red processing unit of the sending station separates 1-bit red data, i.e., "0" or "1" from the RGB data. The black data are sent to the black processing unit of the receiving station over eight parallel signal lines. The red data is sent to the red processing unit over a single signal line. On receiving the black data, the black processing unit at the receiving station modulates a laser diode. The red processing unit of the receiving station modulates an light emitting diode (LED) array on the basis of the 1-bit red data.
Another conventional data transfer device for the above application uses red data having two bits. In this kind of device, two signal lines are assigned to red data. The red processing unit of the receiving station modulates the LED array on the basis of the 2-bit red data.
As stated above, the conventional data transfer devices transfer color data of each color over an exclusive line. Hence, even when black data have, e.g., only 255 levels ranging from "0" to "254", nine lines are needed since the number of bits is eight. It follows that the number of lines cannot be reduced even when the width of data to be sent is small. Moreover, in the case of a color digital copier and a color printer, red data and black data are not transferred at the same time due to the mechanism particular to an electrophotographic process. As a result, either of the two lines is simply wasted.